It was narrated that Jabir bin Samurah said:

"The Messenger of Allah ﷺ came out to us and we were raising our hands during the Salah. He said: 'Why are you raising your hands while praying, like the tails of wild horses? Stay still when you are praying.'"

أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا عَبْثَرٌ، عَنِ الأَعْمَشِ، عَنِ الْمُسَيَّبِ بْنِ رَافِعٍ، عَنْ تَمِيمِ بْنِ طَرَفَةَ، عَنْ جَابِرِ بْنِ سَمُرَةَ، قَالَ خَرَجَ عَلَيْنَا رَسُولُ اللَّهِ ﷺ وَنَحْنُ رَافِعُو أَيْدِينَا فِي الصَّلاَةِ فَقَالَ " مَا بَالُهُمْ رَافِعِينَ أَيْدِيَهُمْ فِي الصَّلاَةِ كَأَنَّهَا أَذْنَابُ الْخَيْلِ الشُّمُسِ اسْكُنُوا فِي الصَّلاَةِ " .